Abstract
In this study, bulk ultrafine-grained and micro-crystalline cobalt was prepared using a combination of high-energy ball milling and subsequent spark plasma sintering. The average grain sizes of the ultrafine-grained and micro-crystalline materials were 200 nm and 1 μm, respectively. Mechanical properties such as the compressive yield strength, the ultimate compressive strength, the maximum compressive deformation and the Vickers hardness were studied and compared with those of a coarse-grained as-cast cobalt reference sample. The bulk ultrafine-grained sample showed an ultra-high compressive yield strength that was greater than 1 GPa, which is discussed with respect to the preparation technique and a structural investigation.
Highlights
IntroductionResearch on nano-crystalline (with grain sizes between 10 and 100 nm) and ultrafine-grained (with grain sizes up to 500 nm) polycrystalline metals and alloys has evolved considerably over the last few decades [1,2,3]
Research on nano-crystalline and ultrafine-grained polycrystalline metals and alloys has evolved considerably over the last few decades [1,2,3]
The structure of the cobalt sample prepared using a combination of ball milling and subsequent spark plasma sintering is visible. It consists of particles with an average size of approximately 100 μm and residual pores, which are shown as black spots and dots
Summary
Research on nano-crystalline (with grain sizes between 10 and 100 nm) and ultrafine-grained (with grain sizes up to 500 nm) polycrystalline metals and alloys has evolved considerably over the last few decades [1,2,3]. These materials exhibit unique properties that are lacking in their coarse-grained counterparts. There are two basic methods of producing these materials; one is top-down, and the other is bottom-up. The bottom-up method involves either one-step processes such as electrodeposition or two-step preparation, which consists of nanoparticle synthesis followed by consolidation [10]. We used a combination of these two approaches
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